New York City Mayor Bill de Blasio urged residents to brace for dangerous conditions.

"The city is facing some of the coldest temperatures and wind chills we've seen in the last 20 years," de Blasio said. "Extremely cold weather can be life-threatening -- especially for seniors, infants and people with medical conditions."

The mayor thanked first responders.

"I think, the combination of the way New Yorkers have heeded the warnings, and the fact that our first responders are out constantly scanning for anyone who might need help, it's been very effective. And thank God, we have no reports to date of any fatalities," he said.

Parts of the South under the gun

Even the South isn't immune to the frigid winter weather.

Another storm is expected to develop Monday in the Southeast and then move to the Northeast by Tuesday.

The heaviest snow will likely fall from Tennessee to the interior Northeast, meteorologists said, especially near the eastern Great Lakes and higher elevations of the Appalachians.

Deadly pileup

At least three people died in the pileup on Interstate 78, Pennsylvania State Police said. More than 70 people were injured.

"It was definitely a whiteout. I couldn't see any farther than probably two city blocks," Raoul Jardine of Allentown said.

"I saw brake lights and pulled off to the side. Somebody hit me when I was parked in the shoulder."

Parts of I-78 were still closed Sunday morning.

Elsewhere on Sunday, a part of Interstate 65 in Indiana was closed after an estimated 40 vehicles were involved in a series of crashes. Several injuries were reported, but none were thought to be life threatening.

"The roadways throughout Central Indiana are snow covered and hazardous. Only travel if necessary, reduce your speed significantly and allow ample space between you and the vehicle in front of you," state police said in a statement.

Frostbite concerns

With the coldest weather of the season, the National Weather Service issued a warning about the symptoms and dangers of frostbite.

When frostbite strikes, ice crystals can form on the skin. Then the skin starts feeling warm, even though it hasn't defrosted, the weather agency said.

After that, the skin can have a waxy appearance and turn red, pale or white, the NWS said. Finally, frostbitten skin can turn dark blue, black or gray, and cause pain that can last for hours.